This invention generally relates to telephone status detection, and in particular to a system and method for detecting an off hook condition of an extension telephone for an adjunct device.
In Call Waiting Caller ID (Type 2 Caller ID) reception, the Caller ID signal is sent to the telephone line while the telephone is off-hook. This signal may be too loud and noisy to the user on an extension phone, and the user""s speech from the extension phone may corrupt the data. To avoid this situation, the CPE (Customer Premises Equipment) such as a Caller ID adjunct device, shall be able to check whether the extension phone is off-hook after a CAS tone (CPE Alerting Signal) is received. If an extension phone is off-hook, the CPE shall not send the ACK tone (Acknowledge Signal) and the Caller ID reception cycle can be terminated. This is recommended by industry standards such as those described in TIA/EIA-PN-4078 documents. In this specification, an xe2x80x9cauxiliaryxe2x80x9d telephone is defined as a telephone connected directly to a CPE. An xe2x80x9cextensionxe2x80x9d telephone is a telephone that is connected to the same telephone line that the CPE is connected to, but not directly to the CPE. This is illustrated, for example, in FIG. 1, where telephone 2 is an example of an extension telephone and telephone 3 is an example of an auxiliary phone.
The present inventors recognize the need for a CPE, such as a Caller ID adjunct, to have the following capabilities for implementing Type 2 Caller ID. An adjunct shall be able to detect an extension phone off-hook condition before replying to the CAS message with an ACK tone. An adjunct shall be able to distinguish extension off-hook (i.e., a phone in other room is in use) from the auxiliary phone off-hook (i.e., the phone attached to an adjunct is in use). An auxiliary phone line shall be muted and the keyboard of an auxiliary phone shall be disabled during the ACK tone and up to the end of FSK data (Caller ID data) reception, as stated in the TIA/EIA-PN-4078. In addition, during the whole Type 2 CID cycle, the telephone line shall be held off-hook all the time. Momentary on-hook cannot exceed 8 ms, as stated in TIA/EIA-PN-4078. Furthermore, if no extension telephone is off-hook, the ACK tone must be sent within a 100 ms time limit after the end of the CAS tone, as stated in TIA/EIA-PN-4078. Therefore the extension off-hook check must be completed and established within the 100 ms time constraint.
One possible approach to solving the above problems may be to perform an extension telephone off-hook check by temporarily-switching the CPE itself on-hook, as in TIA/EIA-PN-4078. The present inventors recognize the disadvantage of this method is that the on-hook period is limited to 8 ms as stated in TIA/EIA-PN-4078. For an adjunct CPE, if the attached auxiliary phone is switched on-hook, there will be transients generated on the phone line and on the CPE""s line checking circuitry. Therefore, the 8 ms time is quite short to let the transient noise settle in order to make a valid extension off-hook check. Also, 8 ms is too short for a line monitoring circuitry to reach a reasonably steady state for an ADC (Analog to Digital Converter) input. Moreover, in case there is speech or electrical noise present on the phone line, the ADC accumulation shall be given as long as possible a period of sampling time in order to produce a more accurate averaged value.
Therefore, in accordance with the present invention, a system and method for detecting a condition of an extension telephone is presented for processing caller ID information. A reference value of a telephone line connected to an apparatus is first determined. An auxiliary telephone connected to the apparatus is then disconnected. A second value of the telephone line is determined while the auxiliary telephone is disconnected. The reference value and the second value of the telephone line are compared to determine the condition, such as off-hook, of the extension telephone.